Electric conductor



March 8, 1949. s. A. DuvALL ELECTRIC CONDUCTOR sl -i1-.ll ......:.......v...

Patented Mar.v s, 1949 Y ELECTRIC CONDUCTOR Stanley A. Duvall, Chicago, Ill., assignor to Runzel Cord & Wire Company, Chicago, Ill., a corporation of Illinois Application July 24, 1944, Serial No. 546,236

5 Claims.

The invention relates to an improvement in electric conductors and in means for preventing or delaying the :breaking of such conductors in use.

One purpose is to provide protecting means for electric conductors employing tinsel wires or other weak conductors, used for example in telephone cords.

Another purpose is to provide protecting means which permit exure of cords and conductors such as telephone cords, while preventing endwise strain on the individual conductors.

Another purpose is to provide a method of forming telephone cords and the like.

Other purposes will appear from time to time throughout the course of the speciiication and claims.

The invention is illustrated' more or less 4diagrammatically in .the accompanying drawings, wherein: Y

Figure 1 is a general view of a telephone cord with parts broken away;

Figure 2 is a section on an enlarged scale along the line 2-2 of Figure 1;

Figure 3 is a section on a still larger scale along the line 3-3 of Figure 2;

Figure 4 is a detail;

Figure 5 is a section on a still largerv scale along the line 5-5 of Figure 4;

Figure 6 illustrates the inner parts of a variant form, some parts being shown in section; and

Figure '7 is a section along the line 'I-1 of Figure 6.

Like parts are indicated by like characters throughout the specification and drawings.

Referring to the drawings I generally indicates any suitable telephone plug having a hollow outer housng 2. 3, 3 indicate a plurality of conductors which may be of any suitable wire such as tinsel or the like. Each such conductor or group of conductors is surrounded by a plurality of lappings or layers 4 of fabric or thelike. 5 indicate fabric spacers of cord or the like. 3a indicates a dummy, used when only two conductors are necessary. The conductors, with their outer portions 4 and the spacers 5, are Wound or twisted together, as shown at the left hand end of Figure 2, to form a spiral group. The composite cord thus formed is surrounded by a layer of fabric or braid indicated at 6. The initial covering 6 may extend from end to end of the cord. The cord thus formed may be produced by the thousands of yards and is the stock or material employed to complete the final cord or connection for the telephone instrument or telephone plug. It may be cut off to the desired length of several feet and is then ready for the formation of the nal cord element.

In making the nal cord, a coil or armor of reinforcing material 9, such as is shown in detail in Figure 4, is wound about the exterior layer 6. It may be preformed as a coil and then wound about the cord in any suitable Way. 0r under some circumstances it may be wound from strip, or extruded, and formed directly about the cord. Preferably, it is curved in cross section, as shown in Figure 5, with the edges engaging the cord and the intermediate convex portion facing outwardly. The cord is fairly closely spaced, the width of the gap between adjacent ends of the helix varying substantially. In the drawings, I illustrate the gap as about one-third the width of the stock of which the helix is formed. It is important, however, that the clearence be suflicient to prevent overlapping of adjacent helix edges, when the cord is bent. The concavity of the material makes the helix grip the covering 6. The edges also are rounded to prevent cutting of the material by the edges of the helix. This rounding is shown at 9a in Figure 5.

After the coil or helix 9 has been positioned about the exterior layer 6 of the cord, a fabric layer I0 is started from the point Illa, a little beyond the end of the helix most remote from the telephone plug. Any suitable machine may be employed for forming or applying the layer I0, which is then carried to the end of the cord as at lub. It will be understood, of course, that the conductors extend beyond the end of the cord. The layer I0 is then continued in reverse to form an outer layer II which is carried to the very end of the nal telephone cord as at IIa.

. At the plug end of the cord I illustrate outwardly extending conductor ends I2, I3 which may be conductively connected. For example, in a two wire cable, the extension I2 as shown in Figure 2 is connected as at I4 to be in conductive relationship with the tip I5 of the plug. The extension I3 is grounded on the plug body 2. For example the plug 2 may have an inwardly screw threaded enlargement 2a the interior of which engages the stripped conductor portion I3a and wedges it against the exterior of the cable. At the opposite end of the cable are any suitable conductor connections such as are shown at I6.

Referring to Figures 6 and '7 I employ individual shields 20 about the outer wrappings 2| of any suitable conductors 22. The shields 20 are shown as extending about more than 180 of arc but are so proportioned and disposed that their edges do not engage. It will be understood that the arcuate extension and the form and length may be widely varied. By extending them about more than 180 of arc I make it possible to snap them about the individual cable conductor elements as shown in Figures 6 and 7. It will be understood that thereafter the cord element will be completed as shown in Figures l and 2 by the application of the outer layers l0, Il or their equivalents, any suitable fillers, such as are shown at 5 in Figure 3, being employed. I may employ light gauge metal or any other suitable material. It will be understood also that l may apply the shields or protectors 20 to a single cable component, or omit it from some components, as desired.

The use and operation of the invention are as follows: r

The primary problem involved is to prevent or delay the breaking of physically delicate electric conductors, such as tinsels, which have for years been used in telephone cords. Tinsel conductors have been in long use in telephone practice, on switchboards and also on desk and receiver cords. Considering the problem as applied to switch board cords, it will be understood that the cord which is secured to the plug I is subject to heavy wear and frequent flexure. The cord is subjected both to compression when the plug is being pushed into the jack and to tension when the plug is being pushed into the jack and to tension when the plug is being drawn from the jack. Also it is subjected to frequent and violent ilexure. This combination of stresses tends to break the tinsels.

I find it desirable to attack the problem both from the angle of reducing flexure and from the angle of reducing endwise stress. The helix shown at 9 in Figure 4 accomplishes both results. In the first place, the helix, somewhat concaved as at 9b, and gripped firmly between the inner layer 6 and the outer layer l0, serves as a reinforcement to take endwise strain from the individual tinsel conductor strands. The concaving of the helix 9 causes its edges to interlock with the surrounded fabric. It provides an efficient means for resisting endwise strain whether of compression or tension. It also is to a considerable extent effective to limit flexure while permitting sulcient ilexure for ready handling of the cord. This limitation of the ilexure reduces the tendency of the tinsels to break. The fact that the employment of the helix provides a corrugation to the cord, makes the cord easier to handle. The reinforcement herein described may be applied without substantial change in the outer diameter of the cord and does not prevent ready insertion of the cord into the plug.

As to the form of Figures 6 and 7, the shields or protectors 20 have a substantial effect in taking up endwise strains in the cord and also someway limit the iiexure of the individual conductors.

It will be understood that the protecting elements 9 and 20 may be made of a substantial variety of materials. I find it advantageous to employ thin metal, I may for example employ a thin metal strip which is turned down to make it thin and which is provided with the rounded edges shown at 9a in Figure 5. I may also employ suitable plastics and under some circumstances may form the strip 9 or the shields 20 by extrusion. I may even employ relatively still' fabric. Where I employ a metal such as steel for the armor or protective parts, I find it advantageous to treat the steel to provide a thin enamel coat.

4 In both forms of the device, the metal reinforcement, the helix 9 of Figures 1 and following, or the members 20 of Figures 6 and 7 are .anchored to the plug by the compression which i any substantial longitudinal tension on the conductors in the cord, while permitting relatively free flexure of the cord.

. It will be realized that whereas I have shown and described an operative device, still many changes might be made in the size, shape, arrangement number and disposition of parts without departing materially from the spirit of my invention. I wish, therefore, that my showing be taken as in a large sense diagrammatic rather than limiting me to my precise showing.

I claim:

1. In combination, a telephone cord and a telephone plug having a socket adapted to receive the end of the telephone cord, a reinforced cord portion adapted to extend into said socket, said cord including a plurality of conductors, insulation surrounding them, the reinforced portion of said cord including a helical reinforcement surrounding said insulation, and anchored at longitudinally spaced points, said cord having an outer covering surrounding said reinforcement, and extending, with said reinforcement, into said socket, said reinforcement terminating substantially short of l the free end of the cord itself, said reinforcement being formed of an inwardly concave helical strip the free edges of which are normally out of contact with the adjacent turns of the strip and are adapted to sink into the outer surface of the insulation surrounding the conductors.

2. In combinationa telephone cord and a telephone plug having a socket adapted to receive the end of the telephone cord, a reinforced cord portion adapted to extend into said socket, said cord including a plurality of conductors, insulation surroundinng them, the reinforced portion of said cord including a helical reinforcement surrounding said insulation, said cord having an outer covering surrounding said reinforcement, and extending, with said reinforcement, into said socket, said reinforcement having anchoring projections adapted to penetrate said outer covering and anchoring the reinforcement thereto at longitudinally spaced points, said reinforcement terminating substantially short of the free end of the cord itself.

3. In combination, a telephone cord and a telephone plug having a socket adapted to receive the end of the telephone cord, a reinforced cord portion adapted to extend into said socket, said cord including a plurality of conductors, insulation surrounding them, the reinforced portion of said cord including a helical reinforcement surrounding said insulation, and anchored at longitudinally spaced points, said cord having an outer covering surrounding said reinforcement, and extending, with said reinforcement, into said socket, said reinforcement terminating substantially short of the free end of the cord itself, the outer covering of the cord being continuous substantially from end to end of the cord.

4. In an electric multi-conductor cord for telephones and the like, a plurality of insulated conductor wires twisted together to form a cable body, a fabric jacket enclosing said cable body to hold the twisted wires together, a relatively stiff flexible helical armor strip encircling the cable body and jacket, the armor strip being longitudinally curved, the opposed edges of the strip being continuously in engagement with the jacket through their entire length.

5. In an electric multi-conductor cord for telephones and the like, a plurality of insulated conductor Wires twisted together to form a cable body, a fabric jacket enclosing said cable body to hold the twisted wires together, a, relatively stiff flexible helical armor strip encircling the cable body and jacket, the armor strip being longitudinally curved, the opposed edges of the strip being continuously in engagement with the jacket through their entire length, an outer cover encircling the jacket and the helical strip and extending from end to end thereof, the cover en- REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 243,162 Sawyer June 21, 1881 278,635 Townsend May 29, 1883 930,896 Speer Aug. 10, 1909 1,155,460 Barbour Oct. 5, 1915 1,177,307 Craven Mar. 28, 1916 1,744,091

Wrape Jan. 21, 1930 

